A brief review of loxapine found no conclusive evidence that it was particularly effective in patients with schizophrenia.[8] A subsequent systematic review considered that the limited evidence did not indicate a clear difference in its effects from other antipsychotics.[9]
Available forms
Loxapine can be taken by mouth.[10] It is also available as an intramuscular injection and as a powder for inhalation.[7][10]
Side effects
Loxapine can cause side effects that are generally similar to that of other antipsychotic medications. These include, e.g., gastrointestinal problems (like constipation and abdominal pain), cardiovascular problems (like tachycardia), moderate likelihood of drowsiness (relative to other antipsychotics),[11] and movement problems (i.e. extrapyramidal symptoms [EPS]).[12] At lower dosages its propensity for causing EPS appears to be similar to that of atypical antipsychotics.[13] Although it is structurally similar to clozapine, it has much lower risk of agranulocytosis (which, even with clozapine, is 0.8%); however, mild and temporary fluctuations in blood leukocyte levels can occur.[14][15] Abuse of loxapine has been reported.[16]
The inhaled formulation of loxapine carries a low risk for a type of airway adverse reaction called bronchospasm that is not thought to occur when loxapine is taken by mouth.[7]
Pharmacology
Mechanism of action
Some scientists say loxapine is a "mid-potency" typical antipsychotic.[15] However, unlike most other typical antipsychotics, it has significant potency at the 5HT2A receptor (6.6 nM), which is similar to atypical antipsychotics like clozapine (5.35 nM). The higher likelihood of EPS with loxapine, compared to clozapine, may be due to its higher affinity for the D2 receptor compared to clozapine, which has one of the lowest binding affinities at the D2 receptor of any antipsychotic.[15]
Values are Ki (nM). The smaller the value, the more strongly the drug binds to the site.
Pharmacokinetics
Loxapine is metabolized to amoxapine, as well as its 8-hydroxy metabolite (8-hydroxyloxapine).[3] Amoxapine is further metabolized to its 8-hydroxy metabolite (8-hydroxyamoxapine), which is also found in the blood of people taking loxapine.[19] At steady-state after taking loxapine by mouth, the relative amounts of loxapine and its metabolites in the blood is as follows: 8-hydroxyloxapine > 8-hydroxyamoxapine > loxapine.[19]
The pharmacokinetics of loxapine change depending on how it is given. Intramuscular injections of loxapine lead to higher blood levels and area under the curve of loxapine than when it is taken by mouth.[19]
Chemical structures of loxapine and clozapine, with key differences highlighted.
Related Research Articles
Antipsychotics, also known as neuroleptics, are a class of psychotropic medication primarily used to manage psychosis, principally in schizophrenia but also in a range of other psychotic disorders. They are also the mainstay together with mood stabilizers in the treatment of bipolar disorder.
Clozapine is the first atypical antipsychotic medication to be discovered. It is usually used in tablet or liquid form for people diagnosed with schizophrenia who have had an inadequate response to other antipsychotics or who have been unable to tolerate other drugs due to extrapyramidal side effects. It is also used for the treatment of psychosis in Parkinson's disease. In the US it is also licensed for use in patients with recurrent suicidal behaviour associated with schizophrenia or schizoaffective disorder. It is regarded as the gold-standard treatment when other medication has been insufficiently effective and its use is recommended by multiple international treatment guidelines. Compared to other antipsychotic drug treatments, initiating and maintaining clozapine is complex, expensive and time-consuming. The role of clozapine in treatment resistant schizophrenia was established by the Clozaril Collaborative Study Group Study #30 in which clozapine showed marked benefits compared to chlorpromazine in a group of patients with protracted psychosis and who had already shown an inadequate response to other antipsychotics. There are a range of different adverse effects and compulsory blood monitoring is required in most developed countries. Whilst there are significant side effects, clozapine remains the most effective treatment when one or more other antipsychotics have had an inadequate response, and clozapine use is associated with multiple improved outcomes including all cause mortality, suicide and reduced hospitalisation. In a network comparative meta-analysis of 15 antipsychotic drugs clozapine was significantly more effective than all other drugs. Surveys of patient satisfaction show preference over other antipsychotics.
Typical antipsychotics are a class of antipsychotic drugs first developed in the 1950s and used to treat psychosis. Typical antipsychotics may also be used for the treatment of acute mania, agitation, and other conditions. The first typical antipsychotics to come into medical use were the phenothiazines, namely chlorpromazine which was discovered serendipitously. Another prominent grouping of antipsychotics are the butyrophenones, an example of which is haloperidol. The newer, second-generation antipsychotics, also known as atypical antipsychotics, have largely supplanted the use of typical antipsychotics as first-line agents due to the higher risk of movement disorders in the latter.
The atypical antipsychotics (AAP), also known as second generation antipsychotics (SGAs) and serotonin–dopamine antagonists (SDAs), are a group of antipsychotic drugs largely introduced after the 1970s and used to treat psychiatric conditions. Some atypical antipsychotics have received regulatory approval for schizophrenia, bipolar disorder, irritability in autism, and as an adjunct in major depressive disorder.
Quetiapine, sold under the brand name Seroquel among others, is an atypical antipsychotic medication used for the treatment of schizophrenia, bipolar disorder, and major depressive disorder. Despite being widely used as a sleep aid due to its sedating effect, the benefits of such use do not appear to generally outweigh the side effects. It is taken orally.
Ziprasidone, sold under the brand name Geodon among others, is an atypical antipsychotic used to treat schizophrenia and bipolar disorder. It may be used by mouth and by injection into a muscle (IM). The IM form may be used for acute agitation in people with schizophrenia.
Olanzapine is an atypical antipsychotic primarily used to treat schizophrenia and bipolar disorder. For schizophrenia, it can be used for both new-onset disease and long-term maintenance. It is taken by mouth or by injection into a muscle.
Tetracyclic antidepressants (TeCAs) are a class of antidepressants that were first introduced in the 1970s. They are named after their tetracyclic chemical structure, containing four rings of atoms, and are closely related to the tricyclic antidepressants (TCAs), which contain three rings of atoms.
Aripiprazole, sold under the brand names Abilify and Aristada, among others, is an atypical antipsychotic. It is primarily used in the treatment of schizophrenia, obsessive compulsive disorder (OCD), and bipolar disorder; other uses include as an add-on treatment in major depressive disorder, tic disorders, and irritability associated with autism. Aripiprazole is taken by mouth or via injection into a muscle. A Cochrane review found low-quality evidence of effectiveness in treating schizophrenia.
Amoxapine, sold under the brand name Asendin among others, is a tricyclic antidepressant (TCA). It is the N-demethylated metabolite of loxapine. Amoxapine first received marketing approval in the United States in 1980, approximately 10 to 20 years after most of the other TCAs were introduced in the United States.
A dopamine antagonist, also known as an anti-dopaminergic and a dopamine receptor antagonist (DRA), is a type of drug which blocks dopamine receptors by receptor antagonism. Most antipsychotics are dopamine antagonists, and as such they have found use in treating schizophrenia, bipolar disorder, and stimulant psychosis. Several other dopamine antagonists are antiemetics used in the treatment of nausea and vomiting.
Tiotixene, or thiothixene, sold under the brand name Navane among others, is a typical antipsychotic of the thioxanthene class which is related to chlorprothixene and is used in the treatment of psychoses like schizophrenia and bipolar mania. It was introduced in the United States in 1967 by Pfizer.
Amisulpride is an antiemetic and antipsychotic medication used at lower doses intravenously to prevent and treat postoperative nausea and vomiting; and at higher doses by mouth to treat schizophrenia and acute psychotic episodes. It is sold under the brand names Barhemsys and Solian, Socian, Deniban and others. At very low doses it is also used to treat dysthymia.
Sulpiride, sold under the brand name Dogmatil among others, is an atypical antipsychotic medication of the benzamide class which is used mainly in the treatment of psychosis associated with schizophrenia and major depressive disorder, and sometimes used in low dosage to treat anxiety and mild depression. Sulpiride is commonly used in Asia, Central America, Europe, South Africa and South America. Levosulpiride is its purified levo-isomer and is sold in India for similar purpose. It is not approved in the United States, Canada, or Australia. The drug is chemically and clinically similar to amisulpride.
Zotepine is an atypical antipsychotic drug indicated for acute and chronic schizophrenia. It has been used in Germany since 1990 and Japan since 1982.
Melperone is an atypical antipsychotic of the butyrophenone chemical class, making it structurally related to the typical antipsychotic haloperidol. It first entered clinical use in 1960s.
Perospirone (Lullan) is an atypical antipsychotic of the azapirone family. It was introduced in Japan by Dainippon Sumitomo Pharma in 2001 for the treatment of schizophrenia and acute cases of bipolar mania.
N-Desmethylclozapine (NDMC), or norclozapine, is a major active metabolite of the atypical antipsychotic drug clozapine. Unlike clozapine, it possesses intrinsic activity at the D2/D3 receptors, and acts as a weak partial agonist at these sites similarly to aripiprazole and bifeprunox. Notably, NDMC has also been shown to act as a potent and efficacious agonist at the M1 and δ-opioid receptors, unlike clozapine as well. It was hypothesized that on account of these unique actions, NDMC might underlie the clinical superiority of clozapine over other antipsychotics. However, clinical trials found NMDC itself ineffective in the treatment of schizophrenia. This may be because it possesses relatively low D2/D3 occupancy compared to 5-HT2 (<15% versus 64–79% at a dose of 10–60 mg/kg s.c. in animal studies). Albeit not useful in the treatment of positive symptoms on its own, it cannot be ruled out that NDMC may contribute to the efficacy of clozapine on cognitive and/or negative symptoms.
Cariprazine, sold under the brand names Vraylar,Reagila and Symvenu among others, is an atypical antipsychotic originated by Gedeon Richter, which is used in the treatment of schizophrenia, bipolar mania, bipolar depression, and major depressive disorder. It acts primarily as a D3 and D2 receptor partial agonist, with a preference for the D3 receptor. Cariprazine is also a partial agonist at the serotonin 5-HT1A receptor and acts as an antagonist at 5-HT2B and 5-HT2A receptors, with high selectivity for the D3 receptor. It is taken by mouth.
Aripiprazole lauroxil, sold under the brand name Aristada, is a long-acting injectable atypical antipsychotic that was developed by Alkermes. It is an N-acyloxymethyl prodrug of aripiprazole that is administered via intramuscular injection once every four to eight weeks for the treatment of schizophrenia. Aripiprazole lauroxil was approved by the U.S. Food and Drug Administration (FDA) on 5 October 2015.
↑ Cheung SW, Tang SW, Remington G (March 1991). "Simultaneous quantitation of loxapine, amoxapine and their 7- and 8-hydroxy metabolites in plasma by high-performance liquid chromatography". Journal of Chromatography. 564 (1): 213–221. doi:10.1016/0378-4347(91)80083-O. PMID1860915.
↑ Taylor D, Paton C, Kapur S, Taylor D (2012). The Maudsley prescribing guidelines in psychiatry (11thed.). Chichester, West Sussex: Wiley-Blackwell. ISBN978-0-470-97948-8.
↑ Nordstrom K (2012). "Inhaled loxapine for rapid treatment of agitation in schizophrenia and bipolar disorder: An update". Neuropsychiatry. 2 (3): 253–260. doi:10.2217/npy.12.23. S2CID39718567.
↑ Roth BL, Driscol J. "PDSP Ki Database". Psychoactive Drug Screening Program (PDSP). University of North Carolina at Chapel Hill and the United States National Institute of Mental Health. Retrieved 14 August 2017.
↑ Appl H, Holzammer T, Dove S, Haen E, Strasser A, Seifert R (February 2012). "Interactions of recombinant human histamine H₁R, H₂R, H₃R, and H₄R receptors with 34 antidepressants and antipsychotics". Naunyn-Schmiedeberg's Archives of Pharmacology. 385 (2): 145–170. doi:10.1007/s00210-011-0704-0. PMID22033803. S2CID14274150.
1 2 3 Simpson GM, Cooper TB, Lee JH, Young MA (March 1978). "Clinical and plasma level characteristics of intramuscular and oral loxapine". Psychopharmacology. 56 (2): 225–232. doi:10.1007/BF00431855. PMID417377. S2CID21795809.
External links
"Loxapine". Drug Information Portal. U.S. National Library of Medicine.
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